Hydraulic lift mechanism

ABSTRACT

Double acting telescoping hoists are coupled by a common fluid control system for raising and lowering a platform connected to the hoists. The hoists have expansion and retraction chambers for inwardly and outwardly telescoping the hoists with the areas on which fluid acts being greater in the expansion chambers than in the retraction chambers. The force created by fluid in the retraction chambers causes each hoist to experience substantially the same load thereby enabling them to expand at substantially the same rate. In one embodiment non-concentric shaped spacers separate the telescoping units of the hoists to prevent their rotation.

United States Patent Notenboom [54] HYDRAULIC LIFT MECHANISM [72]Inventor:

Kirkland, Wash. 98033 22 Filed: Mar. 24, 1969 211 App]. 196;; 809,751

1 [52] Cl.- 92/53, 92/165 PR [51] lnt.Cl ..F0lb 7/20 [58] Fieldol'Search ..92/51, 52, 53, 113, 168,165 PR, 7

[56] References Cited UNITED STATE-S PATENTS 2,517,153 8/1950 Wood .Q..92/53 X 2,933,070 411960 Trumper et al.

3,119,455 1/1964 Fuehrer et al ..92/52 X 3,279,755 10/1966 Notenboom eta1. ..92/53 X 3,298,463 1/1967 McIntosh ..92/52 X Leo JtNotenboom, 121Lake Street South, 7

14s] Apr. 4, 1972 Madland ..92/52 Parrett et al. ..92/52 X PrimaryExaminer-Edgar W. Geoghegan Assistant ExaminerLeslie J. PayneAttorney-Seed, Berry & Dowrey [57] ABSTRACT Double acting telescopinghoistsare coupled bya common a fluid ,control system for raising andlowering a platform connected to the hoists. The hoists have expansionand retraction chambers for inwardly and outwardly telescoping thehoists with the areas on which fluid acts being greater in the expansionchambers than in the retraction chambers. The force created by fluid inthe retraction chambers causes each hoist to experience substantiallythe same load thereby enabling them to expand at substantially the samerate. In one embodiment non-concentric shaped spacers separate thetelescoping units of the hoists to prevent their rotation.

5 Claims, 6 Drawing Figures ATTORNEYS Patented April 4, 1972 3Sheets-Sheet 1 lFllGoll I22 I23 I24 Patented April 4, 1972 3,653,302

3 Sheets-Sheet 2 IN VENTOR.

LEO J. NOTENBOOM FIGO 2 BYCT ""1? W- i w a ATTORNEYS Patnted April 4,1972 3,653,302

3 Sheets-Sheet T5 l 82 L 080 A 4 .7, 7,. i E J 7 H4] -70 m] 66 7e 74 7o1 I UM L9 111:3

FIG, 4

INVENTOR. LEO J. NOTENBOOM ATTORNEYS HYDRAULIC LIFT MECHANISM BACKGROUNDOF THE INVENTION When two or more hoists are powered by a single fluidpump a problem arises in connection with the relative expansion rates ofthe hoists. An uneven distribution of the load on the platform resultsin fluid filling the hoist experiencing the lighter load before theother hoist. This causes both hoists to pivot about their bases lockingtheir telescoping elements thereby preventing further expansion orretraction. The problem is overcome by using two pumps to supply fluidindependently of the two hoists but this greatly adds to the costs ofthe lift mechanism.

The foregoing problem is also overcome by using a level sensingmechanism on the platform to generate a correction signal in a servoloop system to vary the fluid flow to one of the hoists to balance theexpansion rate. Also, where a job.

requirement allows, the foregoing problem is avoided by using a singlehoist to bear all the load. A single hoist lift mechanism, however, hasthe problem of rotating when a torque is applied to the platform. Hoistsare commonly made with concentrically fit tubes or barrels which canbear compression loads but not torque because the tubes are loosely fitwithin one another for telescopic movement.

Accordingly, it is an object of the present invention to devise improvedlift mechanisms. This object is accomplished in part by using adouble-acting hoist which offers superior control over expansion andretraction. The hoist of the present invention has expansion chambersfor outwardly telescoping concentrically fit barrels and retractionchambers for inwardly telescoping the barrels. The surface areas withinthe expansion and retraction chambers on which fluid exerts a force toeither expand or retract the hoist (hereafter called lift areas) aredifferent in the two chambers. The lift area of an ex pansion chamber isgreater than the lift area of arretraction chamber. In connection withthe foregoing, it is an object of the present invention to devisetelescopic hoists having expansion units or barrels which telescopeoutwardly in a sequence starting with expansion of the larger outerbarrels followed by expansion of smaller inner barrels and whichtelescope inwardly in the opposite sequence, i.e. starting withretraction of the smaller inner barrels followed by retraction of largerouter barrels.

In the present lift mechanism a plurality of these hoists areoperatively tied together by a novel fluid control mechanism. The fluidcontrol mechanism simultaneously supplies pressurized fluid to both theexpansion and retraction chambers of each of the hoists. Both outwardand inward forces are exerted on the hoists but because the lift areasof the expansion chambers are greater than that of the retractionchamber the telescoping hoists expand. By selecting the downward orinward acting force at the retraction chambers to be substantiallygreater than the force exerted by the load, unequal distribution of theload among the hoists is minimized. Effectively, the hoists experiencethe same downward forces and therefore telescope outwardly atsubstantially the same rate of expansion. Mechanically tying the hoiststo the same elevator platform also aids the hoists to expand and retractat the same rate. Accordingly, it is another object of the presentinvention to devise means for obtaining substantially uniform expansionof a plurality of telescopic hoists.

Yet another object of the present invention is to provide in a multiplelift hoist system a double acting cylinder capable of exerting a forceagainst its own force of expansion. In addition, it is an object of thepresent invention to devise a doubleacting hydraulic hoist wherein afluid such as a hydraulic liquid is introduced into both; chambers ofthe hoistthr ough the same end. This latter objective is accomplished byemploying one inlet means providing passage directly to the expansionchambers and second inlet means adjacent the first providing passageindirectly to the retraction chambers. The

second inlet means being in direct fluid communication with an interiorchamber formed within the innermost barrel of a I hoist which in turn isin direct fluid communication with the retraction chambers.

It is another object of the present invention to devise a telescopichoist capable of resisting rotation of its telescoping components. Thisobject is accomplished by employing nonconcentrically shaped spacers orheaders between the barrels. The nonconcentrically shaped headers permitexpansion and retraction of the barrles but prevent rotation. It is alsoan object to interfit the nonconcentric elements so as to increase thestructural strength of a hoist.

Still another object of the present invention is to provide means in ahydraulic hoist for purging air and other gases from the hoist.

Another object of the present invention is to devise a hydraulic liftmechanism having a load carrying platform and at least two hydraulichoists mounted on a portablefcarriage.

Another object is to provide a load-carrying platform that is compactwhen stored in its lowest position.

Another object is to provide a carriage having a hoistelevated loadcarrying platform, the personnel supporting floor of which may belowered to below the top of the retracted hoist.

DESCRIPTION OF THE DRAWINGS Other objects and features of the presentinvention will be apparent from a further reading of the presentapplication with reference to the drawings which are: 7 a

FIG. 1 is a cross section elevational view of a hydraulic hoist with abreak line therethrough shown in the fully retracted position;

FIG. 2 is a plan view of a hydraulic fluid control system for thepresent lift mechanism;

FIG. 3 is an end elevational view of the hydraulic fluid con trol systemshown in FIG. 2;

FIG. 4 is a perspective view of the present lift mechanism shown in thefully retracted position with an elevator platform resting on asupporting portable carriage;

FIG. 5 is a perspective view of the lift mechanism of FIG. 4 with theelevator platform positioned in a fully extended position; and

FIG. 6 is a plan view of a hoist according to the present inventionhaving nonconcentrically shaped headers for preventing rotation of thebarrels.

DESCRIPTION OF THE INVENTION The hoist of the present invention as shownin FIG. 1 is comprised of innermost barrel 1, intermediate barrels 2, 3and 4 and outer barrel 5. As clearly seen each of the barrels are ofsimilar configuration and of successively smaller diameter enabling thebarrels to telescope outwardly and inwardly relative to one another. Thebarrels are made from open ended steel alloy tubes. Pistons 8-11 cap thelower open ends of the tubes and define in the spaces between them andthe expansion chambers 15-18. The surface of the lower ends of thebarrels provide part of an expansion chamber lift area along with thesurfaces of the pistons. All the barrels, except outer barrel 5, areturned on a lathe to form the shoulders 20. Headers 21-24 are welded orotherwise fixed to the barrels 2-5 as shown and define retractionchambers 26-29 along with shoulders 20.

Plug 31 caps the upper open end of inner barrel 1 defining with piston 8interior chamber 32 within the inner barrel. Fluid communication isestablished between an external fluid source and the retraction chambersby the telescopic inlet conduit 33 extending through pistons 8-12 intointeriorchamber 32 and by holes 34 drilled in the walls of the barrelsbeneath the shoulders 20. Fluid communication is established between anexternal fluid source and the expansion chambers 15-18 by inlet conduit35 and bores 37 drilled through all but the inner piston 8.

Inlet conduit 33 remains in fluid communication with interior chamber 32as the barrels expand from the fully retracted position shown in FIG. 1to a fully extended position. The telescoping conduit 33 hasfour pipes38-41 of similar configuration and successively larger diametertelescopically interfitted'. The lower ends of the two intermediatepipes 39 and 40 and of the inner pipe 37 are anchored to intermediatepistons 9-11' and outer piston 12 respectively. Appropriate fluid sealsare incorporated at the anchor points of each pipe. Pipes 39, 40 and 41start moving upward with upward movement of piston 11, pipes 40 and 41continue to rise with the movement of piston and pipe 41 continues torisewith movement of piston 9 maintaining a fluid passageway to theinterior chamber 32 at all stages of expansion of a hoist.

Piston rings 43 are fitted about each barrel in appropriate slots 44below the shoulders 20 to form a fluid'seal for the retraction chambers.Beneath piston rings 43 are piston rings 45 and wear strips 46 fittedinto appropriate slots in the barrels to provide additional sealing andan adequate bearing surface. Wiper strips 47 are seated inappropriateslots in headers 21-24 to create a seal to prevent foreign objects fromgetting inside the hoist. Seals 42 create a fluid seal for the upperends of the retraction chambers.

To outwardly telescope the barrels 1-4, fluid is pumped into the hoistthrough inlet conduit 35. The term fluid is intended to include bothliquids and gases since the hoist can be adapted to operate in responseeither to a gas or liquid. The presently preferred fluid is a hydraulicoil liquid. The fluid fills the outer expansion chamber 18 and flows tothe remaining chambers -17 through the bores 37 in the pistons 9-12. Theforce exerted by the fluid on piston 11 is the greatest because of itsgreater surface area due to its size. Piston 11 is therefore movedupward by the force exerted on it, carrying with it barrel 4 to which itis welded and carrying with it also the successively smaller barrels1-3. Barrel 4 moves outwardly relative to barrel 5 until its shouldercontacts header 24. As long as fluid is continued to be pumped into thehoist, the force on piston 10 continues to raise barrels 1-3 until theshoulder 20 on barrel 3 contacts header 23. This process of expansioncontinues until the shoulder on the inner barrel 1 contacts header 21.

Air and other gases are purged or expelled from the expansion chambersduring the initial introduction of a hydraulic liquid into the hoist.The fluid, in this case a liquid, forces gases through the check valve48 into interior chamber 32. Chamber 32 has a venting valve 49 mountedin plug 31 through which the gases escape when the interior chamber isfilled with the hydraulic liquid. Valve 49 is closed when chamber 32 isfilled with the fluid and remains closed during operation of the hoist.

Retraction or inward telescoping of a hoist begins with the innerbarrel 1. Fluid is pumped into interior chamber 32 through telescopicinput conduit 33. The fluid flows through the hole 34 in the innermostbarrel 1 to retraction chamber 26. The fluid pressure acts on thesurfaces of header 21 coupled to the adjacent larger barrel 2 and theshoulder 20 on barrel 1 causing barrel 1 to retract into barrel 2. Thesurface area in retraction chamber 26 on which the fluid exerts a force,i.e. the lift area, is less than that of the lift area of expansionchamber 15. Likewise the lift areas of the other retraction chambers areless than the lift areas of their corresponding expansion chambers. Thisis apparent from inspection of FIG. 1 illustrating the larger surfaceareas of the pistons relative to the headers and shoulders. The mannerin which this difference in lift area is employed in a lift mechanism ismore fully explained below.

' 1 passes hole 34 of barrel 2 allowing fluid to flow into retracti onchamber 27. The fluid in retraction chamber 27 causes barrels l and 2 toretract into barrel 3. Fluid passes to the remainingretraction chambersin like manner until the barrels reach the fully retracted position ofFIG. 1.

In the lift mechanism of the present invention as illustrated in FIGS. 4and 5, two of the foregoing described hoists 52 and 53 are coupled tocarriage 54 and operate together to raise and lower platform 55. A fluidcontrol system 56 is located on the carriage in housing 57. The fluidcontrol system is in fluid communication with hoists 52 and 53 causingthem to expand and retract at substantially the same rate to avoidlocking'of their telescoping components, i.e. the barrels. Platform 55being mechanically tied to the two hoists aids in helping to maintaintheir expansion and retraction rates substantially thesame. Duringexpansion of the hoists fluid is simultaneously supplied to theexpansion and retraction chambers of the hoists. The force generated bythe fluid in the retraction chambers of the two hoists are substantiallythe same giving the hoists equal loads against which fluid in theexpansion chambers work. The force created in the retraction chamber isdesigned to be generally much larger than the force exerted by the load.Therefore, unequal distribution of a load between the two hoists doesnot cause a substantial difference in the expansion rate of the twohoists.

The fluid control system includes conduits 60-63 coupled to theexpansion and retraction chamber inlet conduits 33 and 35 on hoists 52and 53. Conduits 60 and 62 are coupled to the expansion chamber inletson the two hoists. Reservoir 65 contains the fluid for the liftmechanism and may be any suitable hydraulic oil as commonly employed.The fluid is pumped from the reservoir by an appropriate constantdisplacement pump and motor 66 first passing through filter 67. The pumpmaintains the pressure of fluid delivered to the system at apredetermined constant level. Conduit 68 couples the filter to theintake of pump 66. Conduit 70 couples the outlet of pump 66 to mixerjoint 71. Check valve 70a is coupled to conduit 70 to limit thedirection of fluid flow solely to the direction from the pump to themixer joint. Mixer joint 71 is coupled to the retraction chamber inletconduits 61 and 63. The mixer joint is constructed from output T-joint72, input T-joint 73 and output elbow 74. The output elbow of the mixerjoint is coupled to passive joint 76. The passive joint is a T-jointpipe connector coupled at its stem to output elbow 74 and at its arms tothe expansion chamber inlet conduits 60 and 62.

Switching means are provided to control the direction of fluid flow toand from the expansion and retraction chambers of the hoists and therebycontrol their inward and outward expansion. The switching means includesthe four solenoid operated spool or diaphragm valves -83. The spool ordiaphragm valves are two position valves which are normally closedpreventing fluid flow through them. When the solenoids on the valves areenergized by a suitable electrical energy source the valves open to passfluid. Spool valves 80 and 81 are coupled in series with inlet conduits60 and 62 between the hoists and passive joint 76. Spool valves 82 and83 are coupled to reservoir 65 in parallel with the conduits 60 and 62.T- joints 85 and 86 are coupled to conduits 60 and 62 and to conduits 87and 88. Conduits 87 and 88 are coupled in series with the spool valves82 and 83 and meet at venting joint 90. The venting joint is coupled tothe expansion chambers of the two hoists in parallel with the passivejoint.

Venting joint 90 is a four-way pipe connector with left and rightorifices coupled to the conduits 87 and 88 respectively. The lowerorifice is coupled to conduit 91 which terminates at reservoir 65. Theupper orifice of the venting joint is coupled to conduit 92 having handoperated valve 93 coupled in series with it with its handle in itsnormally off position. The valve prevents passage of fluid when thehandle is in the 05 position and passes fluid when the handle is turnedclockwise 90 to an on position.

Conduit 92 terminates in by-pass joint 95. The by-pass joint is aT-joint connector connected to conduit 92 at its stem and to conduits 96and 97 at its arms. Conduits 96 and 97 are in turn connected to thestems of T-joints 98 and 99 connected by their arms to the expansionchamber inlet conduits 60 and 62 between T-joints 85-86 and spool valves80 and 81. The by-pass joint is coupled to the expansion chambers of thetwo hoists in parallel with both the passive and venting joints. Handoperated valve 93 is coupled between the by-pass and venting joint andprovides an auxiliary means for retracting the hoist by providing apassage for bleeding fluid from the expansion chambers that by-pass thespool valves 8083.

The electrical energy source for operating the solenoids on valves 80-83is contained in housing 101. The four electrical connector bundles 102extend from the circuitry in housing 101 to the solenoids on the valves80 83. The solenoids on valves 80 and 81 are electrically coupled inseries to simultaneously energize them and the solenoids on valves 82and 83 are likewise coupled in series. The electrical circuitryincludesa switch to alternately couple the energy source to either of the twopairs of solenoids. The operation of this switch is controlled from amanually operated switch preferably located on platform 55 of the liftmechanism. Placing the manual switch to one position energizes thesolenoids of valves 80 and 81 and deenergizes solenoids of valves 82 and83 for outward telescoping the hoists. Placing the manual switch to asecond position deenergizes the solenoids of valves 80 and 81 andenergizes the solenoids of valves 82 and 83 for inward telescoping thehoists.

With valves 80 and 81 open (their solenoids energized) and valves 82 and83 closed (their solenoids deenergized),fluid is pumped from conduit 70to mixer joint 71 and passive joint 76 enabling fluid pressure to buildup in the expansion and retraction chambers of hoists 52 and 53. Withthe hoists fully retracted, the fluid pressure in the expansion chamberscauses the barrels to begin movement in the sequence discussed earlier.The fluid in the retraction chambers is displaced by the upward movementof the barrels. The displaced fluid is not vented to the reservoir butis combined with the fluid from conduit 70 at mixer joint 71. Therefore,pressure is developed in the fluid in the retraction chamber whichexerts a force on the barrels against which the fluid in the expansionchamber works to telescope the hoists outwardly. The force in theretraction chamber is less than that of the expansion chambers. Theforces are proportional to pressure and lift area and because the liftareas of the expansion chamber are greater the hoists expand. Conduits61 and 63 are smaller in diameter than conduits 60 and 62 and conduit 70is larger in diameter than any of the conduits 60-63.

The lift mechanism is designed such that the force generated in theinner retraction chambers of hoists 52 and 53 is at least as large asthe greatest load expected to be elevated. During expansion, therefore,each hoist works against a sufficiently large force such that anyunequal distribution of the load on platform 55 has a negligible effecton the expansion rate of the hoists.

Pump 66 is shut off when the platform is raised to the desiredelevation. Conduit 104 is coupled to a pressure release valve in pump 66to release excessive pressures.

The platform is retracted by opening valves '82 and 83 (energizing theirsolenoids) and closing valves 80 and 81 (deenergizing their solenoids).Fluid is pumped into mixing joint 71 but flows only to the retractionchambers of the hoists because valves 80 and 81 are closed. The pressureof the fluid in the retraction chambers creates a force which retractsthe barrels of the hoists in the sequence of inner barrels first asdescribed earlier. The fluid in the expansion chambers is displaced andvented through valves 82 and 83 and vent joint 90 to the reservoir.Platform 55 includes a floor 105 for supporting personnel and protectiveupright side walls 106 which may be of heavy wire mesh or the like. Thehoists 52 and 53 are mounted in inverted generally U-shaped brackets 107such that the floor 105 is suspended below the upper ends of the hoists.As is readily apparent, the floor of the platform can be raised andlowered over a wide range of vertical positions. One particularadvantage is that by lowering the floor below the top ends of the hoistsworkmen are able to work comfortably beneath low structures or machines,such as aircraft or the like.

Carriage 54 includes upper frame 108, lower frame 109 interconnected bywelded support struts 110. Ladder 11 1 assists an operator to enter theplatform. The motor and other hydraulic pumping of the fluid controlsystem 56 is contained in the housing 57 supported by the lower carriageframe 109. Tongue 1 13 pivots downwardly to permit attachment to atowing vehicle. Floor jacks 114 are lowered to the ground raising thecarriage off casters 1 15 to stabilize the lift mechanism duringoperation. The entire lift mechanism can be installed on the bed of atruck or other vehicle if desired.

FIG. 6 is a plan view ofa hoist such as that in FIG. 1 wherein headers117-120 corresponding to headers 21-24 are nonconcentrically shaped toresist rotation of the barrels relative to one another. Barrels 122126correspond to barrels 1-5 in FIG. 1 and have shoulders corresponding toshoulders 20 in FIG. 1 beneath headers 117-120 similarlynonconcentrically shaped to define the retraction chambers. Thenonconcentric inner and outer walls of the headers have centers 128 and12 9. The hoist is readily constructed from stock tubing merely'byturning the barrels 122-126 on a lathe about the nonconcentric center129 to form the nonconcentric shoulders. The pistons in this case capthe lower end of each barrel and form, along with the nonconcentricallyshaped lower ends of the barrels, the surface on which fluid acts toexpand a hoist. Likewise, the headers are turned on a lathe to obtaintheir nonconcentric shape. A non-rotating hoist is therefore madepossible using simple components adapted to ease of construction.Aligning the interfitted barrels such that the thickest side of thebarrels and headers are positioned in line to one side of the hoistcreates not only a non-rotating hoist but a hoist with superiorstructural strength. This hoist is capable of bearing greater loads whenoriented away from vertical because the thickness of the materials inthe hoist is greater on one side.

It is believed that the invention will have been clearly understood fromthe foregoing detailed description of my nowpreferred illustratedembodiment. Changes in the details of construction may be resorted towithout departing from the spirit of the invention and it is accordinglymy intention that no limitations be implied and that the hereto annexedclaims be given the broadest interpretation to which the employedlanguage fairly admits.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A telescopic fluid operated hoist comprising:

a plurality of open ended barrels of successively smaller diameter withsmaller barrels movably fitted within successively larger barrels, aplurality of pistons of successively smaller diameter for coupling tothe bottom open end of corresponding size barrels supportingsuccessively smaller barrels and defining expansion chambers betweenadjacent pistons and having means for fluid communication between saidexpansion chambers, a plurality of headers of successively smallerdiameter for coupling to corresponding size barrels above correspondingsize pistons positioned between adjacent barrels, a shoulder on theoutside of all but the largest barrel defining with the header coupledto an adjacent larger barrel a retraction chamber therebetween, saidbarrels having means for fluid communication between said retractionchambers, first and second inlet means coupled to the largest piston forfluid communication between a fluid pressure source and said expansionand retraction chambers respectively, and wherein said barrels aregenerally circular in crosssection and are nonconcentrically fittedwithin each other to prevent rotation therebetween by nonconcentricshaped headers with said shoulders shaped to match generally the shapeof said nonconcentric headers.

2. The hoist of claim 1 wherein said barrels and said nonconcentricallyshaped headers are aligned relative to each other such that the thickestportions of the barrels and headers are positioned to the same sideincreasing the structural strength of the hoist.

3. A telescopic fluid operated hoist comprising:

a plurality of open ended barrels of successively smaller diameter withsmaller barrels movably fitted within successively larger barrels, aplurality of pistons of successively smaller diameter for coupling tothe bottom open end of corresponding size barrels supportingsuccessively smaller barrels and defining expansion chambers betweenadjacent pistons and having means for fluid communication between saidexpansion chambers, a plurality of headers of successively smallerdiameter for coupling to corresponding size barrels above correspondingsize pistons positioned between adjacent barrels, a shoulder on theoutside of all but the largest barrel defining with the header coupledto an adjacent larger barrel a retraction chamber therebetween, saidbarrels having means for fluid communication between said retractionchambers,

, and first and second inlet means coupled to the largest pistonforfluid communication between a fluid pressure source and said expansionand retraction chamber respectively, said means for fluid communicationbetween said expansion chambers including bores providing passagewaysfrom below larger pistons to above adjacent smaller pistons and whereinsaid first inlet means includes a fluid conduit coupled to the bore inthe largest piston, said means for fluid communication between saidretraction chambers including holes in the walls of all but the largestbarrel providing passageways between said retraction chambers and aninterior chamber in the smallest barrel defined by a plug capping theupper open end ing valve coupled to said plug capping said interior'chamber, said venting valve being open during initial filling of saidsystem with a fluid introduced through said inlet means forcing unwantedfluids from said expansion chambers through said check valve into saidinterior chamber and with a fluid introduced through said second inletmeans forcing .unwanted fluids in said interior chamber through saidventing valve thereby purging the hoist of unwanted fluids.

4. A telescopic fluid operated hoist comprising:

a plurality of barrels of successively smaller dimensions with smallerbarrels interfitted within larger barrels allowing movement relative toeach other for expanding and retracting said hoist, means for definingexpansion chambers between adjacent barrels. and for establishing fluidcommunication between said chambers, said expansion chambers having liftareas on which fluid. pressure introduced therein acts to move thebarrels of said hoist, each of said barrels being eccentrically mountedin said next larger barrels such that rotation of a smaller barrelwithin a larger barrel is precluded.

5. The hoist of claim 4 said barrels having headers confining the outersurfaces of the next smaller barrels, said next smaller barrels beingeccentric to said confining headers.

1. A telescopic fluid operated hoist comprising: a plurality of openended barrels of successively smaller diameter with smaller barrelsmovably fitted within successively larger barrels, a plurality ofpistons of successively smaller diameter for coupling to the bottom openend of corresponding size barrels supporting successively smallerbarrels and defining expansion chambers between adjacent pistons andhaving means for fluid communication between said expansion chambers, aplurality of headers of successively smaller diameter for coupling tocorresponding size barrels above corresponding size pistons positionedbetween adjacent barrels, a shoulder on the outside of all but thelargest barrel defining with the header coupled to an adjacent largerbarrel a retraction chamber therebetween, said barrels having means forfluid communication between said retraction chambers, first and secondinlet means coupled to the largest piston for fluid communicationbetween a fluid pressure source and said expansion and retractionchambers respectively, and wherein said barrels are generally circularin cross-section and are nonconcentrically fitted within each other toprevent rotation therebetween by nonconcentric shaped headers with saidshoulders shaped to match generally the shape of said nonconcentricheaders.
 2. The hoist of claim 1 wherein said barrels and saidnonconcentrically shaped headers are aligned relative to each other suchthat the thickest portions of the barrels and headers are positioned tothe same side increasing the structural strength of the hoist.
 3. Atelescopic fluid operated hoist comprising: a plurality of open endedbarrels of successively smaller diameter with smaller barrels movablyfitted within successively larger barrels, a plurality of pistons ofsuccessively smaller diameter for coupling to the bottom open end ofcorresponding size barrels supporting successively smaller barrels anddefining expansion chambers between adjacent pistons and having meansfor fluid communication between said expansion chambers, a plurality ofheaders of successively smaller diameter for coupling to correspondingsize barrels above corresponding size pistons positioned betweenadjacent barrels, a shoulder on the outside of all but the largestbarrel defining with the header coupled to an adjacent larger barrel aretraction chamber therebetween, said barrels having means for fluidcommunication between said retraction chambers, and first and secondinlet means coupled to the largest piston for fluid communicationbetween a fluid pressure source and said expansion and retractionchamber respectively, said means for fluid communication between saidexpansion chambers including bores providing passageways from belowlarger pistons to above adjacent smaller pistons and wherein said firsTinlet means includes a fluid conduit coupled to the bore in the largestpiston, said means for fluid communication between said retractionchambers including holes in the walls of all but the largest barrelproviding passageways between said retraction chambers and an interiorchamber in the smallest barrel defined by a plug capping the upper openend of the barrel and the piston coupled to the smallest barrel, saidsecond inlet means includes a telescoping multi-stage fluid conduitextending through said pistons into said interior chamber for couplingto a fluid source at a position adjacent said first inlet means forfluid communication between a fluid source and said interior chamberthroughout expansion and retraction of said barrels, including a checkvalve positioned in said interior chamber coupled to a bore through thesmallest piston and a venting valve coupled to said plug capping saidinterior chamber, said venting valve being open during initial fillingof said system with a fluid introduced through said inlet means forcingunwanted fluids from said expansion chambers through said check valveinto said interior chamber and with a fluid introduced through saidsecond inlet means forcing unwanted fluids in said interior chamberthrough said venting valve thereby purging the hoist of unwanted fluids.4. A telescopic fluid operated hoist comprising: a plurality of barrelsof successively smaller dimensions with smaller barrels interfittedwithin larger barrels allowing movement relative to each other forexpanding and retracting said hoist, means for defining expansionchambers between adjacent barrels and for establishing fluidcommunication between said chambers, said expansion chambers having liftareas on which fluid pressure introduced therein acts to move thebarrels of said hoist, each of said barrels being eccentrically mountedin said next larger barrels such that rotation of a smaller barrelwithin a larger barrel is precluded.
 5. The hoist of claim 4 saidbarrels having headers confining the outer surfaces of the next smallerbarrels, said next smaller barrels being eccentric to said confiningheaders.